The goal of this pilot project is to define the contribution of voltage-gated, L-type Ca2+ (CaL) channels to the pathogenesis of pulmonary hypertension (PH) in the neonate. Using a well established model of hypoxia-induced PH in neonatal piglets, in-vivo hemodynamics revealed an increased resting pulmonary tone in neonatal piglets exposed to chronic hypoxia (CH) for 21 days. Studies in isolated, perfused lungs from the same CH piglets demonstrated that nifedipine-sensitive CaL, channels contributed to the anomalous vascular tone, and an elevated density of CaL current was observed in patch-clamped vascular smooth muscle cells from small pulmonary arteries. Subsequent studies revealed a striking upregulation of the pore-forming alpha1C subunit of the CaL channel in the pulmonary vasculature of CH piglets, which corresponded to an increased expression of the ancillary p2a subunit that promotes CaL channel trafficking. Interestingly, this same pattern of CaL channel abnormalities was induced in cultured small pulmonary arteries by thromboxane A2 and endothelin-1, two vasoconstrictor substances implicated in neonatal PH. Finally, prophylactic therapy to lower thromboxane A2 availability in 21-day CH piglets prevented the upregulation of CaL channels in the pulmonary vasculature and mitigated the development of PH. Based on these key findings suggesting that the upregulation of CaL channels by vasoconstrictor substances contributes to neonatal PH, we will pursue specific aims designed to: (a) identify the molecular composition of CaL channels in small pulmonary arteries of neonatal piglets, (b) define the mechanistic basis by which thromboxane A2 and endothelin-1 upregulate CaL channels in small pulmonary arteries of CH piglets, and (c) determine if thromboxane A2 and endothelin-1 upregulate CaL channels in the pulmonary vasculature in vivo to contribute to the development of PH. These studies will provide the first detailed information on the stimuli and mechanisms that promote abnormal CaL, channel expression in the pulmonary vasculature during neonatal PH, and will assist in identifying therapeutic targets to mitigate PH in infants and young children.